In construction applications it is important to protect building components from water intrusion and moisture related damage. Cementitious articles, such as gypsum board and cement board, are useful in a variety of applications, some of which require a degree of water resistance. Thus, for such applications, it is often desirable to use a cementitious article faced with a glass or polymer-based fiber mat instead of paper. It also is advantageous to use additives in the cementitious core that improve the water resistance of the core material itself. However, to improve water resistance the mat-faced gypsum board or cement board comprising, consisting of, or consisting essentially of gypsum-based core and fibrous mat is provided with a coating of hydrophobic finish. The fiber mat has an inner surface facing at least one face of the gypsum-based core and an outer surface opposite the inner surface. The hydrophobic finish faces the outer surface of the mat. The major components of the hydrophobic finish are Class C fly ash to promote bonding of finish materials, film-forming polymer and preferably silane compound for water resistance.
However, a drawback of the hydrophobic finish is that it can stiffen too quickly and interfere with operation of industrial production equipment such as roller coaters.
Stiffening of the hydrophobic finish coating leads to buildup on the roller coater and coating delivery system, which makes extended production run difficult. Further, buildup of coating material on the rollers makes it difficult to produce uniform coating with satisfactory application rate and product appearance.
It would also be desirable if the hydrophobic finish coating was capable of being applied to a substrate both in industrial manufacturing operations as well as in the field on construction job sites.
It would also be desirable to achieve improved water resistance with less hydrophobic finish coating.